A standardization-setting organization 3GPP of WCDMA (Wideband Code Division Multiplexing Access) is studying and specifying a communication system that succeeds a “WCDMA system”, an “HSDPA (High-Speed Downlink Packet Access) system”, an “HSUPA (High-Speed Uplink Packet Access) system”, and the like, namely, an “LTE (Long Term Evolution) system”.
In a radio access system of the LTE system, an “OFDMA (Orthogonal Frequency Division Multiplexing Access) system” is defined for a downlink, and an “SC-FDMA (Single-Carrier Frequency Division Multiple Access) system” is defined for an uplink (for example, see Non-Patent Literature 1).
The OFDMA system is a “multicarrier transmission system”, which is configured such that each frequency band (carrier) is divided in plural narrow frequency bands (sub-carriers) and communication is performed using each narrow frequency band (sub-carrier). According to the OFDMA system, the sub-carriers are closely arrayed while orthogonalizing in a frequency axis, so that it is expected that high-speed transmission can be implemented to enhance a use efficiency of a frequency.
The SC-FDMA system is a “single-carrier transmission system”, which is configured such that the frequency band (carrier) of one carrier frequency is allocated to each of plural mobile stations UE (user devices) and the communication is performed using the carrier. According to the SC-FDMA system, an influence of interference between the mobile stations UE can be simply and effectively reduced, and a fluctuation in transmission power can be decreased. Accordingly, the SC-FDMA system is suitable from the viewpoint of low power consumption of the mobile station UE and coverage enlargement.
In the LTE system, the plural mobile stations UE are configured such that the communication is performed while one or at least two physical channels are shared by the mobile stations UE in both the uplink and the downlink.
The channel shared by the mobile stations UE is generally called a “shared channel”. In the LTE system, the shared channel is called a “PUSCH (Physical Uplink Shared Channel)” in the uplink, and the shared channel is called a “PDSCH (Physical Downlink Shared Channel)” in the downlink.
For a transport channel, the shared channel is called a “UL-SCH (Uplink Shared Channel)” in the uplink, and the shared channel is called a “DL-SCH (Downlink Shared Channel)” in the downlink.
In the mobile communication system in which the shared channel is used, it is necessary to select to which mobile station UE the shared channel is allocated in each sub-frame (in the LTE system, 1 ms), and it is necessary to transmit a signal that the shared channel is allocated to the selected mobile station UE.
In the LTE system, a control channel used to transmit the signal is called a “PDCCH (Physical Downlink Control Channel)” or a “DL L1/L2 Control Channel (Downlink L1/L2 Control Channel)”.
The processing of selecting to which mobile station UE the shared channel is allocated in each sub-frame as described above is generally called “scheduling”. The expression that “the shared channel is allocated” may be expressed as “a radio resource is allocated for the shared channel”.
Examples of information transmitted by the PDCCH include “downlink scheduling information” and “uplink scheduling grant”.
Examples of the “downlink scheduling information” include allocation information on a downlink resource block related to the downlink shared channel, information on a UE-ID, the number of streams, or a precoding vector, and information on a data size, a modulation system, or a HARQ (hybrid automatic repeat request).
Examples of the “uplink scheduling grant” include information on an uplink resource block related to the uplink shared channel, information on the UE-ID, the data size, the modulation system, or an uplink transmission power, and information on a demodulation reference signal in an uplink MIMO.
The “downlink scheduling information” and the “uplink scheduling grant” may collectively be called DCI (Downlink Control Information).
The 3GPP studies an LTE-advanced system that is of the communication system succeeding the LTE system. Requirements of the LTE-advanced system are summarized in Non-Patent Literature 2.
That “CA (Carrier Aggregation)” is performed is agreed as one of the requirements in the LTE-advanced system. The “CA” is a technology of performing simultaneous communication between the mobile station UE and the radio base station using a “CC (Component Carrier)” that is of the plural carriers having different carrier frequencies.
For example, in the case that the “CA” is set to be performed in the uplink, the mobile station UE is configured to be able to transmit an uplink signal using the plural “CCs”, and the radio base station eNB is configured to be able to receive the uplink signal using the plural “CCs”.
For example, in the case that the “CA” is set to be performed in the downlink, the radio base station eNB is configured to be able to transmit a downlink signal using the plural “CCs”, and the mobile station UE is configured to be able to receive the downlink signal using the plural “CCs”.